Isidora Morganach

I was recently watching a YouTube video of a girl playing Hogwarts legacy, I haven’t played in a while and she was doing this task that I’m unfamiliar with, or just don’t remember. Isidora morganach being a little girl, I just realized that she may possibly be a muggleborn, considering her family is unfamiliar with magic, and her father told her “it was just in her head”. That makes me wonder…if our character is muggleborn? I always wanted to know the story behind our character, and why she started in her fifth year, as did Isidora and Professor Rackham, and why it is always fifth year. Anyone have any theories?